Dear @Kazuya.Nishiyama,
Yes, I agree.
Best regards,
Dear Jason.
Thank you for your answer.
I have calculated the matrix by varying the NacYIner and HubIner in the fst file and calculated in BModes, but the natural frequencies do not change. Is this normal? (I have not changed the weight.)
I would like to increase the natural frequencies of the tower, is there any other way than the following?
1,Increase the weight of the hub and nacelle
2,Increase the stiffness of the tower
Dear @Kazuya.Nishiyama,
I would expect a change to the tower-top mass and inertia properties to influence the natural frequencies calculated by BModes.
To increase the tower frequency, you could either decrease the mass/inertia of the tower and/or tower-top, increase the stiffness of tower, or shorten the length of the tower.
Best regards,
Dear Jason.
Thank you for your response.
・Is it possible to analyze with the effect of gravity in BModes?
・The area of the hollow circle is needed to determine the mass per unit length of the tower.
In the EXCEL sheet for WP1.5MW, this is calculated as π x diameter x thickness.
What is the difference between this and finding the hollow circle area = 1/4 x (diameter^2-(diameter - thickness x 2)^2)? (The values are slightly different.)
Dear @Kazuya.Nishiyama,
Here are my responses:
Regarding BModes, gravity is not accounted for, which is why you must include gravitational restoring directly in the stiffness matrix if you are using BModes to derive mode shapes and natural frequencies of a tower atop a floating platform.
Regarding the mass per unit length, your second formula appears to be missing a factor of pi. Once this is corrected, these formula are equivalent for thin-walled structures (as the thickness approaches zero), but the latter formula works for cross sections of any thickness.
Best regards,